Method and device for remote sensing of objects

ABSTRACT

The invention relates to a method and a device for remote sensing of objects, said method including the steps of marking said objects with at least one label (10) comprising at least one electrical resonant circuit (14) having an induction means (11) and a capacitor means (12), exciting said resonant circuit (14) to resonance at a resonant frequency, and detecting said resonant frequency of said resonant circuit (14) by the electromagnetic energy transmitted from said resonant circuit (14). An element (13) of a magnetic material having a varying permeability is coupled inductively to said induction element (11). The resonant frequency of said resonant circuit (14) is affected by the permeability of said element (13) of magnetic material, and said element (13) of magnetic material is exposed to an external and spatially heterogenous magnetic bias field through which the permeability of said element (13) of magnetic material is controlled. The invention relates also to methods for coding labels and for noise suppression of signals received from said labels.

BACKGROUND OF THE INVENTION

The invention relates to a method and a device for remote sensing ofobjects. Within trade and industry the interest in non-optical andnon-contact sensing of objects have increased lately. In stores andsuperstores it is interesting to read price labels and similar elements,and within the industry it is desirable to read identification labels inindustrial materials flows. A plurality of non-optical and non-contactprinciples of identification of labels are used at present. Most commonis perhaps antitheft labels in shops.

In a commonly used embodiment in trading, labels are used which areprovided with a resonant circuit comprising a capacitive and aninductive element. Said resonant circuit can be forced to resonance byapplying an electromagnetic signal having a defined energy content atthe resonant frequency to said label in an interrogation zone normallyprovided at the exit of the shop. A detection device detecting signalsfrom said resonant circuit at the resonant frequency produces an alarmif a label provided with an "activated" resonant circuit enters intosaid interrogation zone. A practical embodiment of a resonant circuitintended for this purpose is disclosed in U.S. Pat. No. 4,578,654. Acomplete system includes also a device for "deactivating" said labelwhich is done on payment of the merchandise on which the label isattached to.

A problem of all previously known labels used for the purpose oflimiting pilferage is a lack of ability of individually identifying eachlabel when a plurality of labels is present simultaneously in saidinterrogation zone. For the purpose mentioned the problem is notrelevant because an alarm should be delivered independently if one or aplurality of labels having an "activated" resonant circuit enters intosaid interrogation zone and is detected.

SUMMARY OF INVENTION

The method according to the present invention is based on the fact thatcertain magnetic and mechanical properties of elements shaped as tapes,wires or strips of amorphous materials are changed when the elements areexposed to a magnetic field, a so called bias field. Theposition/direction of an element is for instance related to the magneticfield in the longitudinal or axial direction of the amorphous element,and the mechanical resonant frequency of the element is a measure of theposition/direction of the element. Corresponding conditions apply for acomponent comprising an amorphous element which is magnetically coupledto an inductive element in turn included in an electrical resonantcircuit. When the magnetic field is changed the magnetic properties ofthe amorphous element are changed, and by that the inductance of saidinductive element is changed. Then also the resonant frequency of theelectrical resonant circuit is changed.

Also materials other than amorphous materials can be used according tothe invention. The essential property of the material is that thecharacteristics thereof, for instance magnetic or elastic properties,are effected by magnetic fields. The influence must have such an extentthat the change of properties is measurable by remote detecting, i.e.without establishment of a physical contact with said elements. It isalso possible to use other materials, the electric or magneticproperties thereof being changed by an external magnetic field. Anexample is a material that is magnetoresistive, that is the electricalconductivity thereof being changed depending on a magnetic field, and amagnetooptical material, that is a material the light conducting abilitythereof is changed depending on an applied magnetic field. For materialsof said latter type a phenomenon referred to as the FARADY EFFECT isutilized, that is that the plane of oscillation of polarized light ispivoted, the pivoting angle being proportional to the magnetic fieldstrength, or the phenomenon referred to as the KERR EFFECT, according towhich a similar effect appears in some materials under influence of anelectrical field.

The resonant frequency of an amorphous element showing a comparativelylarge magnetomechanical coupling is changed by the so calleddelta-E-effect with the magnetic flux intensity along the main directionof the element. If said magnetic flux intensity is changed as a functionof the position/direction of said amorphous element the resonantfrequency of said amorphous element will then be a function of theposition/direction of said element. It is an advantage that themeasuring information is produced as a frequency value because such avalue is highly immune to interferences. Furthermore, a mix ofinformation from a plurality of gauges, each of which operates at aseparate frequency band, can be transferred together at one channel ofinformation.

To increase the measuring precision it is possible also to utilizemethods according to which a plurality of amorphous elementssimultaneously are located in a measuring body. In such a case it isappropriate also to record beat frequencies and sum frequencies. Byutilizing such differential measuring methods error sources such as forinstance system deviation depending on temperature, material properties,changes of field, etc., can be eliminated.

It should be noted that the efficient magnetic field along the axialdirection of said amorphous element is not necessarily equal to theprojection of the total field vector along the amorphous element. By theflux conductive ability of said amorphous element and the geometrythereof there could be a deviation from pure projection. However, therelationship can always be determined and could still form the bases ofrecording objects that are provided with amorphous elements.

By using tapes of amorphous magnetoelastic alloys in a theft protectionlabel it is possible also to use other physical effects and conditions.A theft protection label of this type will include one or a plurality ofsuch tapes. Said tapes have a high magnetomechanical coupling whichmeans among other things that the tapes can be made to oscillatemechanically by applying magnetic energy. During the mechanicaloscillation also the magnetic properties change, which can be recordedby a detecting coil or similar device. An essential factor of theresonant frequency of the tape is the module of elasticity. Since themodule of elasticity of the amorphous tapes used depends on externalmagnetic fields it is possible by varying such an external magnet fieldto change the resonant frequency of the tape. By providing a magneticelement that can be magnetized and demagnetized adjacent to a tape of anamorphous material the tape can be given two resonant frequencies, afirst when the magnetic element is magnetized and a second when it isdemagnetized. Such a system is disclosed in EP 0096182. In this type ofsystems it is necessary that the tapes are arranged to be moved freelyin such a way that the mechanical movement during oscillation is notprevented or affected to such a level when a safe detection is indanger. The excitation of the tapes to oscillation as well as thedetection of the resonant frequency is made through magnetic fieldswhich highly limits the range of operation, in the excitation as well asduring detection.

A more developed system for remote sensing of objects is disclosed in EP00330656. Instead of an element of a magnetic material that can bemagnetized and demagnetized, respectively, to set the resonant frequencyof the tape a spatially heterogeneous magnetic field in theinterrogation zone is used according to EP 00330656. In that way aplurality of labels located within different subareas of saidinterrogation zone in which the magnetic field is directed differentlyor is of a different strength can be sensed and identified even if aplurality of labels are provided with identical sets of tapes. However,problems and drawbacks of excitation and detection by means of magneticfields still remain. Also in this type of labels it is important thatthe tapes are arranged on the label to be moved freely. Thus, saidlabels have to be produced, arranged on the objects and be handled in aproper way so that the movability of the tapes is not affected.

An object of the method and device for remote sensing of objects inaccordance with the present invention, is to overcome the drawbacksindicated above by using an electric resonant circuit, and it is also anobject to overcome problems and drawbacks of detection devices includingtapes of a material having a high magnetomechanical coupling. Saidobjects have been achieved according to the invention by marking anobject to be sensed with at least one label including an electricalresonant circuit having an inductive element and a capacitive element.The resonant circuit is excited to oscillate at a resonant frequencywithin the radio frequency spectrum. The resonant frequency of theresonant circuit is detected through the electromagnetic energytransmitted from the resonant circuit. An element of magnetic materialhaving a varying permeability is inductively coupled to the inductiveelement such that the resonant frequency of the resonant circuit isaffected by the permeability of the element of magnetic material.Detection is accomplished by exposing the element of magnetic materialto an external and spatially heterogeneous magnetic bias field tocontrol the permeability of the element of magnetic material.

Developments of the invention with regard to coding of the identity ofsaid labels, and with regard to interference suppression of receivedsignals are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail by means ofembodiments, reference being made to the accompanying drawings in which

FIG. 1 is a schematic view showing the method and the device accordingto the invention,

FIG. 2A shows a first alternative embodiment of a resonant circuit to beused according to the invention,

FIG. 2B shows a second alternative embodiment having double resonantcircuits to be used according to the invention,

FIG. 3 is a diagram showing how the magnetizing field strength dependson the position in an interrogation zone used according to theinvention,

FIG. 4 is a diagram showing the relative permeability of a tape made ofa magnetic material in relation to the magnetizing field strength in theinterrogation zone,

FIG. 5 is a schematic view showing a combined transmitting and receivingantenna to be used according to the method of the invention,

FIG. 6 is a schematic view showing a further development of a device fordetecting objects,

FIG. 7 shows schematically in a perspective view an interrogation zonewith biasing coils,

FIG. 8 is a top view of the device of FIG. 7,

FIG. 9 is a diagram showing a combination of resonant circuits havingdifferent resonant frequencies,

FIG. 10 shows schematically a coding method according to a developmentof the invention,

FIG. 11 shows schematically an alternative coding embodiment accordingto a development of the invention,

FIG. 12 shows a practical embodiment for the method of coding accordingto FIG. 10,

FIG. 13 shows a practical embodiment for a method of coding according toFIG. 11,

FIGS. 14 and 15 are graphical representations showing characteristics ofthe material that can be used according to the invention,

FIG. 16 depicts an inductive element and a magnetic element combined ina web-like structure.

DETAILED DESCRIPTION

FIG. 1 shows a label 10 which is provided with an electric resonantcircuit 14. A label refers according to the invention to any elementsthat can be mounted on or during production be embedded in objects thatcan be remotely detected. The resonant circuit can for instance beembedded in a wall or a surface of the object such as a spine, embeddedin a cavity in a piece of furniture, molded into a plastic part, or in asimilar manner.

The electrical resonant circuit 14, comprises an inductive element 11and a capacitive element 12, and has through said elements an antennafunction. In the embodiment shown in FIG. 1 there is also provided afurther conductor 11a. Said conductor 11a is connected in parallel withsaid capacitive element 12, in this case formed as a capacitor, andconstitutes a part of said inductive element. Said inductive element 11including a coil is inductively coupled to an element 13 made of amagnetic material. Said element 13 is arranged adjacent to or withinsaid coil. Said element 13 is preferably made of a tape of an amorphousalloy. Said element 13 of magnetic material possesses according to theinvention such a property that the permeability thereof will vary by theinfluence of an external magnetic field. By the inductive couplingbetween said element 13 and said coil 11 the resonant frequency of saidresonant circuit 14 depends directly on the magnetic properties, that isthe permeability of said element 13.

To excite said resonant circuit 14 to oscillation at the resonantfrequency of said resonant circuit, which falls within a radio frequencyinterval, an electrical excitation means 15 is provided. Preferably saidexcitation means 15 comprises an electromagnetic antenna which isconnected to a control unit 17 including a transmitting unit not shownhere. An embodiment of an antenna 15 is shows in FIG. 5. To said controlunit 17 there is connected also a detecting means .16 which preferablyalso includes an antenna. To allow a plurality of identical labelshaving identical resonant circuits 14 to be detected, identified andrecorded when they simultaneously are located in an interrogation zonethere is provided a means 18 for producing a magnetic field. Said means18 is operatively connected to said control unit 17 and produces aspatially heterogenous magnetic field varying in strength and/ordirection in each location or subvolume of the interrogation zone. Themagnetic field generated provides a spatial reference system that can beused in different ways according to the invention. A difference ofmagnetic field between adjacent location or subareas within saidinterrogation zone will affect magnetically said magnetic elements 13 ofeach of said resonant circuits so that the relative permeability thereofwill be changed differently. In that way also the property of theinductive elements of said resonant circuits are affected differentlyresulting in different offsets of the resonant frequency of saidresonant circuits. Said offset depends on the characteristics of themagnetic field in the location of said label and said magnetic element,and also on the orientation of the element in space.

FIG. 2A shows an alternative embodiment of said resonant circuit. Thedifference compared to resonant circuit shown in FIG. 1 is that saidconductor 11a has been excluded.

FIG. 2B shows another alternative embodiment including double resonantcircuits 14 and 14' which are connected to a common element 13 made of amagnetic material. The resonant frequencies of said resonant circuits 14and 14' can be made different by applying to the coil 11' and thecapacitor 12' of said second resonant circuit 14' different propertiesthan corresponding components of said first resonant circuit 14. Alsoother alternative configuration of an inductive element 11, a capacitiveelement 12, and elements 13 made of magnetic materials are possiblewithin the scope of the invention. Other configuration can be chosenalso to improve other electrical properties of the resonant circuit suchas Q value, antenna properties, etc.

The physical background explaining why it is possible according to theinvention to identify a plurality of identical labels within theinterrogation zone will now be described with reference to FIG. 3 andFIG. 4. Said means 18 for generating a magnetic field and described inconnection with FIG. 1 generates a spatially heterogenous magnetic fieldin said interrogation zone. Said magnetic field in the interrogationzone will vary with regard to strength and/or direction in differentlocations within the interrogation zone. This is illustratedschematically in FIG. 3 showing the variation of the magnetic fieldstrength in different locations, for instance having different Xcoordinates.

The amorphous material of the tapes that preferably are used accordingto the invention possess such a property that the relative permeabilitydepends on the magnetic field strength H and accordingly on the magneticfield B in the interrogation zone.

FIG. 4 is a graphical representation showing this relation. Theamorphous material has a very high magnetomechanical coupling and thusthe magnetic properties of the amorphous material are affected also bythe mechanical conditions that the tapes of amorphous material areexposed to. The upper diagram line in FIG. 4 marked ₁₀₂ .sup.σ shows howthe relative permeability depends on the magnetic field strength whenthe tape can be moved freely and is allowed to oscillate alsomechanically. The lower diagram line marked .sub.χ ε shows thedependence of the relative permeability on the magnet field strengthwhen the tape of amorphous material is fixedly attached and cannotoscillate mechanically. According to the invention anyone of theconditions indicated can be employed and it is possible also to utilize"double" properties either as a further coding of a label or for settingsaid label from an "activated" condition in which said label in apricing system indicates a merchandise that has not been paid for, and a"deactivated" condition in which said label indicates a merchandise thathas been paid for. Because the magnetic field in the interrogation zonewill vary in all locations or subvolumes all magnetic elements locatedin said interrogation zone will be exposed to a magnetic field ofdifferent strength or direction. In that way the relative permeabilityof said magnetic elements 13 will have different values depending on theposition and orientation of the element in the interrogation zone, andthis will in turn change the electrical properties and the resonantfrequency of said resonant circuit 14. This may be described by therelation L=f(μ_(r)), illustrating that the induction L is a function ofthe relative permeability μ_(r).

In a basic embodiment each of the resonant circuits of all labels has aunique resonant frequency which will identify the label in a basiccondition, that is in a condition with a known and stable magneticfield. Then when the label is disposed in the interrogation zone theresonant frequency of the resonant circuit will be offset. Differentresonant frequencies and maximum variations allowed in the magneticfield from said device 18 are chosen in such a way that the resonantcircuits and thus also the labels of different objects cannot be mixedup by the detecting system 18.

In further developed embodiments a plurality of elements 13 made ofmagnetic material, are combined to make the frequency dependence of theresonant circuit of the external magnetic field more complex and hard tocopy.

Tapes made of amorphous material are extremely direction sensitive, thatis their sensitivity to external influence in the form of externalmagnetic fields, traction and compression strain force, etc., varieshighly with the orientation in relation to the direction in which theexternal force is supplied. Such a condition is used already in thebasic embodiment of a label according to the invention allowing aplurality of identical labels that are oriented in different directionsto be readily separated by the detection system even if they aredisposed in the absolute vicinity to each other. In a further developedembodiment of a label according to the invention a plurality ofidentical tapes of amorphous material or tapes formed in different waysare arranged on top of each other but pivoted in relation to each other.This will allow an extremely extensive and complex coding of a label ina very compact embodiment. An alternative coding method is describedbelow with reference to FIG. 10. FIG. 12 illustrates a practicalembodiment of FIG. 10. To further increase the safety it is appropriatealso to execute a plurality of consecutive detecting steps havingdifferent sequences of heterogenous magnetic bias fields.

The electrical excitation means 15 as well as the detection means 16comprise some kind of antenna for transmitting and receiving,respectively, electromagnetic radiation in form av radio waves. Anexample of a combined transmitter and receiver antenna is shown in FIG.5. A transmitting antenna 19 which is operatively connected to saidexcitation means 15 and formed as a single loop of rectangular shapeencloses a receiver antenna 20 shaped as figure-eight and operating as abalanced frame antenna. Said receiver antenna 20 is operativelyconnected to said detecting means 16. The embodiment of an antennaarrangement shown in FIG. 5 is preferred because transmitting andreceiving at the same frequency is facilitated. Also other more or lessconventionally formed antenna systems can be used within the scope ofthe present invention. The resonant circuit 14 emits energy also withinother frequency intervals than the resonant frequency, for instanceharmonics of the resonant frequency, and thus it is appropriate incertain applications to excite said resonant circuits at one frequencyand to detect oscillations at another frequency.

FIG. 7 shows an example of the arrangement of said interrogation zonewith the means for generating a magnetic field. In the shown embodimentthe heterogenous magnetic field in said interrogation zone 33 isgenerated by four coils 29,30,31,32 which are arranged in pairs in rightangles on different non-opposing sides of the interrogation zone 33. Theorientation of the coils are shown also in FIG. 8 which is a top view ofthe interrogation zone 33 with said coils 29,30,31,32 shownschematically.

On large demands of miniaturization of the label thin fill technique orsimilar techniques can be used to produce the complete label includingthe capacitive element 12 and the inductive element 11 and otherconductors and antenna function included therein. Also coil elements andcapacitors produced as conventional elements can be used in someapplications.

In an alternative embodiment, as illustrated in FIG. 16, said inductiveelement 11 and said magnetic element 13 are connected into a so called"cloth inductor" in which said elements are combined into a web likestructure. This embodiment will provide a high magnetic coupling factorbetween said magnetic element and said inductive element.

In an application for pricing labels each label is provided with nresonant circuits having n different resonant frequencies. The diagramof FIG. 9 shows detected resonant frequencies f_(l) . . . f_(n) from oneof said labels. Each resonant frequency defines one "bit" in a code ofan item. Existence of a specified resonant frequency in the detectedsignal will indicate that the corresponding "bit" is set. The offset ofthe resonant frequency of all resonant circuits depending on the biasfield is known and therefore all resonant circuits that are exposed toone and the same bias field can be related to a specific label. Then thelabel is identified by the combination of resonant circuits, that is ofthe resonant frequencies, giving the code of the item. The resonantfrequencies will vary or be offset within the dashed area in FIG. 9 foreach frequency.

The method and the device according to the invention are very suitableto be used in different applications in connections with marking, forinstance price marking in trade, marking of products withinmanufacturing industry or transport industry, in coding of credit cards,and also in "seal marking" of for instance documents, tickets, etc. Inthe latter application the previously described embodiment, having aplurality of bands of amorphous material together forming a more"complex" transfer function of permeability and external magnetic field,can be used.

The method and the device according to the invention can be applied alsoin determining position and/or orientation. In such an application themagnetic field generated in said interrogation zone is known in detailin every location with any desired resolution. When a measuring objectincluding the resonance circuit according to the invention is enteredinto said interrogation zone and the resonance frequency thereof isdetected by the detecting means 16 the deviation of frequency from anominal resonance frequency of the circuit is an exact indication of theposition of the object in the interrogation zone. A corresponding methodcan be applied also for direct distance measuring. To determine only theorientation a completely homogeneous bias field can be used.

The method and device according to the invention can be used also inother applications and at other frequencies not disclosed here. At lowerfrequencies than radio frequencies the coupling between the label andthe transmitter/receiver is made mostly on the basis of induction. Theembodiments of resonant circuits and control and detection systemsdisclosed above should be regarded only as examples, a plurality ofother embodiments are possible within the scope of the invention asdefined in the accompanying claims.

At least two properties of tapes, wires and similar elements ofamorphous material are affected in a basic way by a surrounding magneticfield. A first property to be affected is the elastic properties of theelement, and in that case the so called delta-E effect is used.Variations of elastic properties affect directly other properties of theelement, for instance the mechanical resonant frequency of the element.The mechanical resonant frequency can be detected as a magnetic signal,for instance by a detecting coil because the magnetomechanical couplingof said element is very large.

The detected signal includes besides the desired signal also differentinterference signals appearing around the measuring site. To be able touse the detected signals as desired when identifying elements anyunwanted signals have to be filtered out or suppressed.

To accomplish a suppression or filtering the following measures can betaken. When an element is exposed to a varying magnetic field strengththe resonant frequency of the element will vary according to thevariation of the field strength. FIG. 14 is a graphical representationshowing delta-E of an element as a function of a magnetic field strengthH. When the magnetic field strength is varied according to a firstfunction the delta-E of the element will vary according to a secondfunction that can be associated to or be identified with said firstfunction. By suppressing all detected signals that are not associated inthis way to said first function it is ensured that only wanted signalsare recorded and further processed.

FIG. 15 shows correspondingly how a second property of an element isaffected, namely the relative permeability μ_(r). Also μ_(r) is afunction of the magnetic field strength H. Any influence on saidrelative permeability is suitably detected by coupling said elementmagnetically to an inductive element included in an electric resonantcircuit which includes also a capacitor. When said resonant circuit isexcited to oscillate it will transmit electromagnetic radiation whichcan be recorded by means corresponding to conventional radio receivers.The frequency of the electromagnetic signal is then affected by thesurrounding magnetic field strength H.

Interference signals appear also in this type of detecting, and it ishighly desirable to suppress interference signals also in this type ofdetecting. This is conveniently done according to a method as indicatedabove.

FIG. 6 shows an embodiment of a device according to the invention. Inthis embodiment said means 18 for generating a magnetic field includes amodulator 25 which modulates the magnetic field generated by said coils29,30,31,32 in accordance with a predetermined function. Said coils29,30,31,32 are fed by a current generating means 26 throughcontrollable amplifiers 27. Said current generating means 26 and saidmodulator 25 are controlled by said control unit 17, which isoperatively connected thereto.

The device comprises also a transmitter antenna 19 and a receiverantenna 20 formed in accordance with the embodiment shown in FIG. 5. Onelabel 10 is located in the interrogation zone. The input signal fromsaid receiver antenna 20 is amplified in a first amplifier 21 and thenin a second amplifier 22 before being fed into a PLL-circuit (PhaseLocked Loop) 23. A frequency output of said PLL circuit 23 is connectedto said transmitter antenna 19 through an amplifier 24. An internal,frequency adjusting signal in said PLL-circuit is tapped and fed to acomparator 34. Said tapped signal referred to as V_(demod) forms ademodulated signal corresponding to the signal generated in a modulatingunit 25 in said means 18 for generating a magnetic field. When the biassignal is not modulated said signal of the PLL-circuit is a measure ofthe present non-modulated resonant frequency. Also the signal generatedin said modulating unit 25 is fed to said comparator 34 so as to comparethe controlling modulating signal from said modulator unit 25 to thedemodulating signal from said PLL-circuit 23. The result of thecomparison is preferably used to filter out any disturbances appearingin the interrogation zone and being received together with the wantedsignal.

To ensure that a received signal originates from an element to beremotely detected it is possible also to sample the received signal thatoriginates from an amorphous element. In a basic embodiment of such amethod the sampled signal defining a received frequency is controlled tovary in time. During correct conditions the received frequency is theresonant frequency of an element. If this is the case the sampled signalis regarded to be a wanted signal and said signal is processed asindicated above to determine any existence of a specific amorphouselement on a label or similar device, and thereby to identify the labeland the object on which the label is attached.

In further developed systems there is a digital signal processing of thesampled signal so as to determine the relation between the variation ofthe bias field and the variation of the sampled signal. Only if therelation meats predetermined standards the received sampled signal ispassed on. The determination of the relation can be made for instance bydividing the received resonant frequency signal intoFourier-coefficients. When these are compared the accordance between thecontrolled signal and the received signal can be determined.

According to an alternative and basic embodiment there is instead made afiltering of the static part of the received frequency signal. If avarying-part remains, that is if the frequency varies, this will beaccepted as a confirmation of the signal originating from an elementwhich has been affected by the bias field.

Different factors will affect the selection of decoding methods. Oneimportant factor is the environment with respect to interferences thatexist in the detection volume.

The bias field can be adjusted with regard to the absolute value of themagnetic field strength and also with regard to the direction of themagnetic field strength.

A further method for ensuring that a received signal originates from anelement to be remotely detected is based on producing distortion in acontrolled and predetermined manner of the signal transmitted from theelement of amorphous material. Then only received signals that have beendistorted in the predetermined way are used for determining existingresonant frequencies.

The signal processing being made on a received signal to suppressunwanted signals is the same independent of the received signal beingmagnetic, when the magnetomechanical coupling of the amorphous elementis used, or electromagnetic, when the influence of the element on anelectric resonant circuit is used.

To provide a coding of labels allowing identification of a plurality oflabels in a detection volume even if a plurality of identical labels islocated in the volume at the same time at least three embodiments arepossible. A first embodiment is similar to a type of binary coding. In afixed set of elements shaped as tapes or wires of amorphous materialelements may be present or be removed corresponding to 1 and 0 in abinary code. The number of tapes is also equal to the number of bitpositions, and the tapes are all different. This would meancomparatively large costs for producing labels and will limit to someextent the total number of possible label identities.

In an alternative coding method a plurality of magnetic elements 13 aredisposed "on top of" each other with an angular deviation and will eachby the angular position thereof constitute a "bit" or a code position.In the embodiment shown in FIGS. 10 and 12 the position system has thebase 10 because each element can be set into one of ten angularorientation positions. Each element 13 is given a unique length/resonantfrequency. When there are a plurality of labels at the same time in adetecting zone the detecting device will read code elements from aspecific label as they are all located in one and the same coordinateposition with different angular orientations in one and the samepivoting plane (if the label is plane). Different labels can beseparated by different x,y,z-position and/or different "pivotingplanes", which means that each label is individually detectable even ifa plurality of identical labels are detected simultaneously.

A major advantage with the second coding method compared to the binarycode indicated above with regard to read reliability is that the numberof amorphous element in the second coding method is always constant (fora specific number interval or base) because the code information is inthe signal relation, that is the frequency relation or angle between thedifferent amorphous code elements, and not in the existence ornon-existence of a specific amorphous element which is the case when thebinary coded label is used. This would mean that the number of amorphouselements that is provided in each label is known, which is not the casein a binary coded label. Then the detecting system can control that allcode elements have been recorded and can also determine if any labellacks any of the elements. This highly improves the validation processduring detection.

Using such a coding method different detecting algorithms can be used.Thess can be divided into algorithms implying that the bias field usedis known and mapped, and such algorithms that do not require knowledgeof the characteristics of the magnetic field. Both methods of detectingcan be used according to the present invention.

According to a coding method the angles between the amorphous elementsof the label are used to define the code position. Thus, each elementcan be set to represent any code value within a predetermined numberinterval. That means that the base can be considerably larger than two,for instance 30. When using the base 30 and on condition that a labelcomprises four coding elements plus a reference element it is possibleto provide code values between 0 and 809999 using five tapes, and ifbinary code is used only values 0-31 can be utilized.

An algorithm for detecting labels having two reference elements and fourcoding elements will now be described. In the description below it isassumed that all tapes in a label have different length so as to bereadily identified separately.

On condition that the local magnetic field distribution over a label ishomogeneous the two reference elements will provide the angle and theabsolute value of the magnetic field vector over said label in the planeof the label. The two right angle components of the bias field aredetermined by using the detected resonance frequency of the elements.The detected resonant frequency corresponds to the bias field along thelongitudinal axes of the elements. Having knowledge about the effectivevalue and the angle of the bias vector in the actual plane the angles ofthe code elements can be determined by utilizing the relation betweendetected frequency and magnetic field. This is done for each codeelement. The value of the bias vector along a code element divided withthe value of the bias vector in the plane determined as indicated abovewill provide immediately, or indirectly as a result of influence ofadjacent elements, through another function, the cosines of the anglebetween a code element and the bias vector. As the angle of the biasvector has been determined it is possible also to determine the angle ofthe code element and thus the code value set for the specific codeelement. The code value determined might be corrected with regard toinfluence from adjacent bands.

However, a problem still remains of relating signals from differentelements to each label. However, it is possible to calculate allpossible combinations of reference and code elements. Among these alsothe correct codes are included together with a large number of noisecodes.

By providing a sequence of different bias field situations andcalculating for each bias field situation all possible codes the correctcodes will be repeated to a completely different extent than the noisecodes. Only those codes that are "repeated" will then be accepted. It isobvious that when a large number of labels is located in the detectionvolume at the same time the number of possible codes will be extremelylarge. To facilitate the analysis of incoming signals it can beappropriate to divide the detection volume into a plurality of smallersubvolumes. Then the number of labels per volume will be lower and thealgorithm for analysis can be executed faster. It is possible also toeliminate a number of possible codes by certain modulation of the biasfield and by using further logical functions.

In an alternative embodiment according to FIG. 11 and FIG. 13 of thecoding method described above the possibility of remote detecting of theangle between elements is not used but instead the possibility of remotedetecting of the relative distance between single elements is utilized.Such an alternative coding method corresponds to some extent to thecommonly used pincode.

One example of such an embodiment comprises a label having a pluralityof elements of different length arranged in parallel on a distance froma reference tape. The distance from said reference tape to the actualdistance of a specific element constitutes a code value of the element.To improve reading possibilities of a label of such a type it isappropriate to arrange also a second reference element on a distancefrom said first reference tape. All other elements are arranged betweensaid reference elements. By using two reference elements it is possiblewhen reading to determine the local field gradiant along the codeelements and the label. Hereby it is possible to read in all regards theinformation of the label without knowing in detail the actual localmagnetic field.

The alternative code method described above has a plurality ofadvantages in relation to the previously described angle code method.For instance all elements are arranged in parallel which means that theefficient bias field applied over a label is more limited or definedthan in the angle coding method. Hereby the reading of the label isfacilitated. A side effect is that all elements probably will be readthrough one and the same detecting channel which will reduce thedistortion during transmission caused by detecting coils and detectingelectronics.

The angle coding method and also the distance coding method describedabove can be utilized at mechanical resonance of the elements anddetecting magnetic field changes as a result of the mechanicalresonance, but also at electrical resonance, wherein the elements areincluded in electrical resonance circuits as magnetic elements coupledto the coil included in said resonance circuit.

We claim:
 1. Method of remote sensing of objects comprising the stepsof:marking said objects with at least one label including at least oneelectrical resonance circuit having an inductive element and acapacitive element; exciting said resonance circuit to oscillate at aresonance frequency within a radio frequency spectrum; and detecting theresonance frequency of the resonance circuit through the electromagneticenergy transmitted from said resonance circuit, the detecting stepincluding the steps of inductively coupling an element of magneticmaterial having a varying permeability to said inductive element,affecting the resonance frequency of the resonance circuit through thepermeability of the element of magnetic material, and exposing saidelement of magnetic material to an external and spatially heterogeneousmagnetic bias field to control the permeability of said element ofmagnetic material.
 2. Method according to claim 1 wherein thepermeability of said element of magnetic material controls the resonancefrequency of a plurality of resonance circuits.
 3. Method according toclaim 1 wherein one element of magnetic material is inductively coupledto inductive elements of at least two electrical resonance circuits. 4.A device for remote sensing of objects, each object being marked with atleast one label including at least one electric resonant circuit havingan inductive element and a capacitive element, said resonant circuitbeing formed to be excited to oscillation at a resonant frequency withinthe radio frequency spectrum, the device comprising:an electricalexcitation means for producing an electromagnetic signal exciting saidresonant circuit; a detecting means, sensitive to electromagneticradiation, for detecting electromagnetic radiation from said resonantcircuit, said resonant circuit including at least one elementinductively coupled to said inductive element, said at least one elementbeing formed of a magnetic material having a varying permeability foraffecting the resonant frequency of said resonant circuit; and amagnetic field generating means for generating, in an interrogationzone, a spatially heterogeneous magnetic bias field by which thepermeability of said element of magnetic material is affected.
 5. Deviceaccording to claim 4, wherein said element of magnetic material ismechanically anchored to prevent mechanical oscillation.
 6. Deviceaccording to claim 4, wherein said label is provided with a combinationof mechanically anchored and mechanically free elements of magneticmaterial.
 7. Device according to claim 4, wherein said electric resonantcircuit comprises a plurality of elements of magnetic material havingdifferent magnetic characteristics.
 8. Device according to claim 4,wherein said label comprises a combination of resonant circuitscollectively forming an item code of the object.
 9. Device according toclaim 4, wherein said means for generating a magnetic field is formed togenerate an adjustably modulated signal for generating a modulated biasfield.
 10. Device according to claim 4, wherein said element of magneticmaterial is made of an amorphous material.
 11. Device according to claim10 wherein said inductive element and said magnetic element are combinedinto a web like structure.
 12. Method for determining in threedimensions the position and orientation of objects marked with at leastone label including at least one electric resonant circuit having aninductive element and capacitive element, the method comprising thesteps of:exciting said resonant circuit to oscillation at a resonantfrequency within the radio frequency spectrum; and detecting theresonant frequency of the resonant circuit by the electromagnetic energytransmitted from said resonant circuit, the detecting step including thesteps of inductively coupling an element made of magnetic material of avarying permeability to said inductive element such that the resonantfrequency of said resonant circuit is controlled by the permeability ofthe element made of magnetic material, exposing the element made ofmagnetic material to an external magnetic bias field which is known inall points with a desired resolution with regard to strength and/ordirection, through which bias field the permeability of said elementmade of magnetic material is affected, and determining the position andorientation of the objects using the resonant frequency detected andcontrolled by said magnetic bias field.
 13. Method of remote sensing ofobjects, comprising the steps of:providing an object with an elementmade of a material, the characteristics thereof being influenced by asurrounding magnetic field; exposing said element to a magnetic fieldstrength H; detecting the influence of the field strength on thecharacteristics by receiving a signal of magnetic or electromagneticradiation from said element; varying the magnetic field strength Haccording to a predetermined function; comparing said received signal tosaid predetermined function; and using any parts of the received signalhaving a predetermined correlation with the predetermined function forthe remote sensing of the object.
 14. Method according to claim 13,wherein the predetermined function is a function varying in time with acertain frequency, said received signal is fed to a Phase Locked Loop(PLL) comprising a voltage controlled oscillator and a phase detector,the output thereof controlling the frequency of the oscillator, theoutput signal of said phase detector being related to the frequency ofthe varying function when said loop has been locked to the receivedsignal, and wherein the output level of the phase detector is comparedto a predetermined level corresponding to a certain frequency of thevarying function, a correlation between the output level and thepredetermined level indicating that the received signal originates froma remotely detected element.
 15. Method according to claim 14, whereinsaid magnetic field strength H is controlled to vary in time and a timevarying part of the received signal is separated and used for the remotesensing.
 16. Method for coding remotely detected labels, comprising thesteps of:providing at least two elements for each label, thecharacteristics thereof being changed by an external magnetic field,said label being exposed to a biasing magnetic field covering adetecting volume that is larger than the label for detecting thecharacteristics of said elements changed by said magnetic field;orienting elements of each label in predetermined mutual relationshipsfor providing an identity to the label determined by said relationshipswhen said elements are exposed to a sequence of different fielddistributions, the local field distribution of the biasing field oversaid label being continuously determined; wherein the mutualrelationship between the elements is determined depending on theorientation of each element in the local field distribution by comparingactual properties of the elements influenced by said magnetic field, andexpected properties of elements arranged in predetermined relationshipsto each other in the local field distribution.
 17. Method according toclaim 16, wherein said elements are elongated, and said elements areoriented in fixed mutual angle relationships with regard to thelongitudinal direction of said elements.
 18. Method according to claim16, wherein said elements are elongated, and said elements are orientedwith fixed mutual distances in a direction transverse to thelongitudinal direction of said elements.
 19. Method according to claim16, wherein the orientation of the elements is determined in relation toa reference element.
 20. Method according to claim 19, wherein the localfield distribution is determined by providing at least two referenceelements on the label, said reference elements being located with aknown mutual orientation.